I tried both and liked both quite well. It is a tough choice and should be made subjectively on the basis of wet test. I our case the Caldera was better for us, but I can fully understand why someone else would choose Hot Spring. Somewhere in the archive you probably can find my analysis of the Envoy versus the Geneva Utopia.
I liked the stronger jets of the Caldera better than the Motomessager of the Hot Spring. My wife is 5-feet tall and I am 6-feet, the small ridge on the bottom of every Caldera helped my wife stay anchored better than any other brand. Frankly I find it helps me too. In addition to these two, we also considered Marquis and Jacuzzi Premium, which are also fine products.
The Envoy and Geneva are very similar in many ways and are obviously made by the same company. The fitration systems are quite different, but in the end I decided that this did not matter as both have sparkling clean water when used in accordance with the instructions. Heaters, pumps, and other features also seem to be quite similar. The shell finish in white pearl looks identical and presumably other colors would be very similar too. The warranties are the same.
In truth these two brands are really top notch and you can't go wrong with either. Pick the one that feels best to you, or pick the dealer that seems better for your area. In my area the price was about the same, but if there is a significant difference where you are, that factor should be weighed carefully in making your decision.
Regards,
Bill